Transport vehicles, in particular rail vehicles, are required to reduce the resistance to motion so as to reduce the size of the traction equipment, and so as to limit energy consumption.
In this way, profiles are sought that are as aerodynamic as possible. Unfortunately, the outside surface of a train has various cavities, such as: gaps between cars, pantograph-receiving bays, and under-body bogie bays, which are all obstacles to train motion, and they increase noise level.
At high speeds, a large portion of the resistance to motion is due to the aerodynamic drag of the vehicles.
A portion of the drag is due to changes in the shape of the outside streamlining of the vehicles, and in particular to cavities. The aerodynamic profile of a train is most modified by the gaps between vehicles in the train and by the bogie-receiving bays.
Known prior art means that enable those problems to be solved consist in placing rubber flaps between the cars so as to provide aerodynamic continuity. A drawback with that solution is that it prevents easy access to equipment. Furthermore, such devices are not reliable over time, and they increase the time that needs to be spent on repair and maintenance. The same applies to bogie-receiving bays and pantograph-receiving bays where fixed or moving streamlining systems mask the cavities. Such streamlining hides equipment to the detriment of safety.
Therefore, the problems posed by this type of cavity are not solved satisfactorily.
Document FR-A-805 960 describes a device for reducing resistance to motion due to gaps or other interruptions in vehicles.
That prior art device consists of at least one deflecting surface disposed on the vehicle at the interruption, in particular at the ends of the cars or other vehicles suitable for being coupled together.
The deflecting surfaces are disposed so that they extend the surface of the vehicle over which the relative air flow slides, and so disposed that they make the relative air flow more uniform by preventing it from penetrating into the interruption where it would otherwise tend to create a turbulence zone.
Prior art document FR-A-805 960 teaches that the deflecting surfaces are placed substantially in the plane of the relative air flow, i.e. so that they extend the walls of the vehicle. The deflecting surfaces may be set back slightly, but, in principle, they must not project outwardly relative to the walls.
As taught by that document, the deflecting surfaces are based on deflecting the air streams outwards. From that document, it can be understood that the deflecting surfaces act as deflectors only and that they have no technical effect on the flow of air inside the cavities.
Document BE-A-417 270 describes equipment for streamlining moving bodies. That equipment includes deflecting surfaces resulting from members whose position can be changed, and which are hinged about rocking axes, so that they can be put into various angular positions, thereby either reducing the resistance to motion of the moving body, or else increasing it.
As taught in that document, the deflecting surfaces are based on deflecting the air streams laterally. From that document, it can also be understood that the deflecting surfaces act as deflectors only and that they have no technical effect on the flow of air inside the cavities.
The problems posed by this type of cavity are not solved satisfactorily for the reasons given below.
It is known that the aerodynamic drag of a cavity depends to a large extent on the ratio .alpha. of its width 1 divided by its depth P.
As indicated in FIG. 1, for a given cavity width 1, the drag is at its minimum when the ratio a has a value that is close to 1. The value of the drag doubles suddenly when the ratio .alpha. is close to 2, it remains approximately constant until the ratio .alpha. is equal to 10, and it then falls off again slowly when the ratio .alpha. is greater than 10.
The cavities considered in the prior art, e.g. those described in the above-mentioned documents have ratios .alpha. lying in the range 2 to 10, and they therefore correspond to the worst cases.
A solution that is difficult to implement consists in closing the cavities.
Another solution consists in bringing the ratio .alpha. to 1. This solution is also difficult to implement because, to do so means either reducing the width l, which is generally imposed by clearances, or else increasing the volume of the cavity, and this reduces the available space inside the vehicle.
Another solution is given in Document FR 91 13 510 to the Applicant.
Document FR 91 13 510 to the Applicant describes means making it possible to reduce the resistance to motion generated by cavities. For each cavity, those means include a profile disposed in the vicinity of the cavity but not facing the cavity, the profile being held at a determined distance from the outside surface of the train, the determined distance enabling said resistance to motion to be reduced.
That solution suffers from the drawbacks that the profiles must be disposed at a relatively long distance from the cavity and at a relatively high height from the wall. That solution involves problems of overall vehicle size, and of clearance outside the vehicle.